1. Field of the Invention
The present invention relates to a display device for displaying a measured value, and in particular, to a technology for analogically displaying a measured value obtained as digital date in real time.
2. Description of the Related Art
In measuring instruments for measuring dimensions, shapes and the like, analog measuring instruments, in which a displacement of a measuring point is enlarged by movement of levers or gears and the displacement amount is read from a pointer on a scale plate, were only mainstream before digital technologies are developed as in today. After that, digital technologies based on semiconductor technologies have been greatly advanced and such digital technologies have been applied to dimension or shape measuring instruments. Also, in terms of detecting principles, as electronic encoders of photoelectric type or capacitance type are developed instead of levers or gears, measuring instruments in which all of detecting and displaying of measured results are digitally performed are developed.
Because such digital measuring instruments display the measured results as numerical values, individual differences in reading or read errors can be greatly reduced to allow a stable and high accurate measurement. In the other hand, however, merits of the analog measuring instruments represented by pointer type are also reappraised. Namely, such digitally displayed numerical values have problems in that instantaneous grasping of a measured result is difficult and additionally because a measured value is meanderingly changed while a measuring point is finely displaced, reading is difficult and grasping of a direction of change, which indicates whether a measured value is being increased or decreased, is also difficult, and the like. Thus, it has been found that analog displaying of pointer type is superior in these respects.
Therefore, digital measuring instruments for analogically displaying a measured value are commercially available. Japanese Patent No. 3372793 discloses a digital and analog display-type dial gage as one example of such digital measuring instruments. The digital and analog display-type dial gage has a dial gage body, a spindle provided to be slidable relative to the dial gauge body, and a liquid crystal display. The liquid crystal display is a custom liquid crystal module having a digital display portion and an analog display portion. A displacement amount of a measuring point provided on a distal end of the spindle is displayed on both of the digital display portion and the analog display portion.
The digital display portion has seven-segmented electrodes for + or − symbol and five digits and a displacement amount of the measuring point is displayed to be directly readable by numerical display. The analog display portion has analog graduation segments, which are analog display graduations and are formed by rod-shaped electrodes arranged to be aligned in parallel to each other, and analog pointer segments, which are pointers for analogically displaying the displacement amount of the measuring point and are formed by a plurality of rod-shaped electrodes arranged to be aligned in parallel to each other, and typically only one analog pointer segment is selectively displayed.
Although grasping of a direction of change in measured value is somewhat facilitated by the analog display portion of the custom liquid crystal module, a mechanical dial gage having an analog indicator constituted of a scale plate and a rotatable pointer allows a measured value to be intuitionally read and thus enjoys a deep-seated popularity even today. To display the analog indicator constituted of the scale plate and the rotatable pointer on a liquid crystal display, a graphic liquid crystal module capable of displaying any figure needs to be used.
However, in a conventional method of displaying the analog indicator constituted of the scale plate and the rotatable pointer on the graphic liquid crystal module, the entire surface of a display screen is sequentially updated. Therefore, an amount of data to be processed for updating of the display screen is enormous, so that it is not easy to rapidly perform updating of the display screen.
JP-A-2011-113041 discloses a display device in which when an analog indicator constituted of a scale plate and a rotatable pointer is displayed on a graphic liquid module, updating of a display screen can be rapidly performed. The display device has a display portion having a plurality of display pixels arranged thereon, a drawing memory for storing each pixel data to be imparted to the plurality of display pixels, and a controller adapted to store the pixel data into the drawing memory by sequentially reading out base image data for displaying the scale plate and pointer image data from a ROM (Read Only Memory) at every frame and then recording the read-out data into the drawing memory. On the basis of the last pointer region in which the pointer is displayed in the last frame, the controller records a partial region of the base image data encompassing the last pointer region as base image data for the current frame. In this configuration, the entire base image data for the current frame is not overwritten, but a partial data thereof based on the pointer region in the last frame is overwritten. Accordingly, a load in recording and processing the base image data for the current frame is reduced and also a recording speed is increased.
In the display device disclosed in JP-A-2011-113041, updating of data on the drawing memory from the last frame to the current frame undergoes an intermediate state (state D shown in FIG. 3 of JP-A-2011-113041 or the like), so that memory-overwriting processing needs to be performed twice. Therefore, there is a room for further speed-up of updating of the display screen.
Further, in the display device disclosed in JP-A-2011-113041, the pointer image data has to be recorded into the ROM at every predetermined angle of the pointer. Namely, a large amount of image data needs to be previously recorded into the ROM.
In the display device disclosed in JP-A-2011-113041, memory-overwriting processing has to be performed twice or a large amount of image data has to be previously recorded even if other graphic display modules, such as a graphic organic EL (Electro Luminescence) module, are used instead of the graphic liquid crystal module.